Processes for forming an aldehyde by the reaction of an olefin with carbon monoxide and hydrogen have been known as hydroformylation processes or oxo processes. For many years, all commercial hydroformylation reactions employed cobalt carbonyl catalysts which required relatively high pressures (often on the order of 100 atmospheres or higher) to maintain catalyst stability.
U.S. Pat. No. 3,527,809, issued Sept. 8, 1970 to R. L. Pruett and J. A. Smith, discloses a significantly new hydroformylation process whereby alpha-olefins are hydroformylated with carbon monoxide and hydrogen to produce aldehydes in high yields at low temperature and pressures, where the normal to iso-(or branched-chain) aldehyde isomer ratio of the product aldehydes is high. This process employs certain rhodium complex catalysts and operates under defined reaction conditions to accomplish the olefin hydroformylation. Since this new process operates at significantly lower pressures than required theretofore in the prior art, substantial advantages are realized including lower initial capital investment and lower operating costs. Further, the more desirable straight-chain aldehyde isomer can be produced in high yields.
The hydroformylation process set forth in the Pruett and Smith patent noted above includes the following essential reaction conditions:
(1) A rhodium complex catalyst which is a complex combination of rhodium with carbon monoxide and a triorganophosphorus ligand. The term "complex" means a coordination compound formed by the union of one or more electronically rich molecules or atoms capable of independent existence with one or more electronically poor molecules or atoms, each of which is also capable of independent existence. Triorganophosphorus ligands whose phosphorus atom has one available or unshared pair of electrons are capable of forming a coordinate bond with rhodium.
(2) An alpha-olefin feed of alpha-olefinic compounds characterized by a terminal ethylenic carbon-to-carbon bond such as a vinyl group CH.sub.2 .dbd.CH--. They may be straight chain or branched chain and may contain groups or substituents which do not essentially interfere with the hydroformylation reaction, and they may also contain more than one ethylenic bond. Propylene is an example of a preferred alpha-olefin.
(3) A triorganophosphorus ligand such as a triarylphosphine. Desirably each organo moiety in the ligand does not exceed 18 carbon atoms. The triarylphosphines are the preferred ligands, an example of which is triphenylphosphine.
(4) A concentration of the triorganophosphorus ligand in the reaction mixture which is sufficient to provide at least 2, and preferably at least 5, moles of free ligand per mole of rhodium metal, over and above the ligand complexed with or tied to the rhodium atom.
(5) A temperature of from about 50.degree. to about 145.degree. C., preferably from about 60.degree. to about 125.degree. C.
(6) A total hydrogen and carbon monoxide pressure which is less than 450 pounds per square inch absolute (psia), preferably less than 350 psia.
(7) A maximum partial pressure exerted by carbon monoxide no greater than about 75 percent based on the total pressure of carbon monoxide and hydrogen, preferably less than 50 percent of this total gas pressure.
It is known in the prior art that rhodium hydroformylation catalysts, such as hydrido carbonyl tris (triphenylphosphine) rhodium, are deactivated by certain extrinsic poisons which may be present in any of the gases fed to the reaction mixture. See, for example, G. Falbe, "Carbon Monoxide in Organic Synthesis", Springer-Verlag, New York, 1970. These poisons (X), termed virulent poisons, are derived from materials such as sulfur-containing compounds (e.g., H.sub.2 S, COS, etc.), halogen-containing compounds (e.g. HCl, etc.), cyano-containing compounds (e.g. HCN, etc.), and the like, and can form Rh-X bonds which are not broken under mild hydroformylation conditions. If one removes such poisons from the materials fed to the reaction mixture, to below 1 part per million (ppm), one would expect therefore that no such deactivation of the catalyst would occur. However, it has been found that such is not the case. For example, when very clean gases (&lt;1 ppm extrinsic poisons) were used in the hydroformylation of propylene and a gas recycle technique (described in commonly-assigned, copending U.S. application Ser. No. 776,934, filed Mar. 11, 1977 now U.S. Pat. No. 247,486) was employed, under the following conditions:
temperature (.degree.C.): 100 PA1 CO partial pressure (psia): 36 PA1 H.sub.2 partial pressure (psia): 75 PA1 olefin partial pressure (psia): 40 PA1 ligand/rhodium mole ratio: 94
the catalyst activity decreased at a rate of 3% per day (based on the original activity of the fresh catalyst). It appears therefore that even the substantially complete removal of extrinsic poisons does not prevent such catalyst deactivation.
Copending, commonly-assigned U.S. patent application Ser. No. 762,336, filed Jan. 25, 1977 now abandoned, in favor of continuation U.S. application Ser. No. 151,293, filed May 19, 1980, indicates that the deactivation of rhodium hydroformylation catalysts under hydroformylation conditions in the substantial absence of extrinsic poisons is due to the combination of the effects of temperature, phosphine ligand:rhodium mole ratio, and the partial pressures of hydrogen and carbon monoxide and is termed an intrinsic deactivation. It is further disclosed therein that this intrinsic deactivation can be reduced or substantially prevented by establishing and controlling and correlating the hydroformylation reaction conditions to a low temperature, low carbon monoxide partial pressure and high free triarylphosphine ligand: catalytically-active rhodium mole ratio. More specifically, this copending application discloses a rhodium-catalyzed hydroformylation process for producing aldehydes from alpha-olefins including the steps of reacting the olefin with hydrogen and carbon monoxide in the presence of a rhodium complex catalyst consisting essentially of rhodium complexed with carbon monoxide and a triarylphosphine, under certain defined reaction conditions, as follows:
(1) a temperature of from about 90.degree. to about 130.degree. C.;
(2) a total gas pressure of hydrogen, carbon monoxide and alpha-olefin of less than about 400 psia;
(3) a carbon monoxide partial pressure of less than about 55 psia;
(4) a hydrogen partial pressure of less than about 200 psia;
(5) at least about 100 moles of free triarylphosphine ligand for each mole of catalytically active rhodium metal present in the rhodium complex catalyst; and controlling and correlating the partial pressure of carbon monoxide, the temperature and the free triarylphosphine:catalytically active rhodium mole ratio to limit the rhodium complex catalyst deactivation to a maximum determined percent loss in activity per day, based on the initial activity of the fresh catalyst. By "catalytically active rhodium" is meant the rhodium metal in the rhodium complex catalyst which has not been deactivated. The amount of rhodium in the reaction zone which is catalytically active may be determined at any given time during the reaction by comparing the conversion rate to product based on such catalyst to the conversion rate obtained using fresh catalyst. The manner in which the carbon monoxide partial pressure, temperature and free triarylphosphine:catalytically active rhodium mole ratio should be controlled and correlated to thus limit the deactivation of the catalyst is illustrated in detail in said application Ser. No. 762,336.
It has been observed that the presence of n-alkyldiarylphosphines (for example, n-propyldiphenylphosphine or ethyldiphenylphosphine) in the rhodium-catalyzed hydroformlation of the alpha-olefin propylene inhibits catalyst productivity; i.e., the rate at which the desired product aldehydes are formed. Specifically, the addition of small amounts of propyldiphenylphosphine or ethyldiphenylphosphine to rhodium hydroformylation solutions (i.e., 250 ppm rhodium and 12% by weight triphenylphosphine in a mixture of butyraldehydes and butyraldehyde condensation products) markedly reduced the rate of production of butyraldehydes from propylene, compared to the rate obtained in the absence of the alkyldiarylphosphines. However, copending, commonly-assigned U.S. patent application Ser. No. 762,335, filed Jan. 25, 1977 now abandoned, in favor of continuation U.S. application Ser. No. 140,830, filed on Apr. 16, 1980, discloses that the stability of such rhodium complex catalysts can be significantly enhanced by providing an n-alkyldiarylphosphine in the reaction medium. More specifically, said application Ser. No. 762,335 discloses improving the stability of the catalyst by providing in the liquid reaction medium containing the catalyst an amount of an n-alkyldiarylphosphine ligand; and controlling the hydroformylation reaction conditions as follows:
(1) a temperature of from about 100.degree. to about 140.degree. C.;
(2) a total gas pressure of hydrogen, carbon monoxide and alpha-olefin of less than about 450 psia;
(3) a carbon monoxide partial pressure of less than about 55 psia;
(4) a hydrogen partial pressure of less than about 200 psia;
(5) at least about 75 moles of total free phosphine ligand for each mole of catalytically-active rhodium metal present in the rhodium complex catalyst. However, a disadvantage of using such n-alkyldiarylphosphines is that they substantially retard the rate of the hydroformylation reaction.
U.S. Pat. No. 3,644,446 discloses hydrido carbonyl complexes of rhodium and iridium with biphyllic ligands of the formula EQU ER.sub.3
wherein E is As, Sb, P, Bi or P(O).sub.3 ; and R is hydrogen, C.sub.1-10 alkyl or C.sub.6-10 aryl. The patentees generally indicate that such complexes have utility as hydroformylation catalysts.
U.S. Pat. No. 4,151,209 discloses a process for hydroformylating an olefin in the presence of a rhodium complex catalyst comprising rhodium in complex combination with carbon monoxide and a triorganophosphorus ligand, wherein progressive deactivation of the catalyst, as well as loss of the ligand species through by-product formation, are reduced by continuously stripping the liquid reaction medium to a degree such that the content of high-boiling organophosphorus by-products therein is maintained at a low level such that the ratio of phosphorus contained in said high-boiling by-products to phosphorus contained in the ligand present in the reaction medium does not exceed about 0.2.